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Full text of "Text Book Of Mechanical Engineering"

784                            Appendix IL

being loose, are afterwards removed horizontally. The top half
of the pattern is similarly treated, by embedding in loani as at
G, and the plates N and P are bolted together to facilitate lifting
and turning over. Here there are two loose flanges as at E, and
the runner and riser patterns, all of which have to be inserted.

The two halves of the main core are next made, the skeleton
being again used; but this time the loam boards are swept
outside it as at H, while the pump barrel is struck by the board j
for the lower half, and by a similar, but shallower, board for the
upper half. The flanges are supplied by pattern r. The two
main cores are, of course, made separately, and in order to remove
them the guiding strips for board j must be only temporarily
fixed, and the skeleton itself must also be split at the same
place. The cylinder core is struck on an iron barrel (seep. 14),
and cores are provided for the holes K K, Q, &c.

Lastly, the various parts of the mould are put together : first
the lower cope, then the lower core, the cylinder core, upper
core, and the upper cope, inserting the before-mentioned short
cores, and thus making ready for casting.

P. 31. Steam Cylinder in G-reensand.óCylinders of
the smaller size cannot be moulded in loam like that on p. 21, so
a short account is here given of a greensand mould, aided by Pig.
764. The pattern is split horizontally through the centres of
steam chest and barrel, and is supplied with prints B and c to
secure withdrawal of the lower half, the sand pockets A, B, and c,
being afterwards filled by cores made in suitable boxes. A. core
u is also moulded for the steam chest, and the barrel core is struck
on a pipe M, as already described at p. 14; j showing the straw
rope, and u the loam covering. Examining the direction of
withdrawal of the upper half of the pattern, shewn by the arrow,
the steam and exhaust-pipe flanges are seen to be troublesome
parts. This is a case where some care in design would obviate
much after expense, for the flanges could easily be made to
draw if the pipes were equal to them in diameter; as shewn
however, they are loose on the pattern, and a third box is pro
vided for their subsequent withdrawal. One other method, at
F, requires ring cores between flange and cylinder body. The
port cores L L, pipe cores ft. and K, and stuffing-box cores D D>